The present invention relates to a method of manufacturing a tailgate to a pickup truck and especially to a method of making a molded polymer tailgate.
Pickup trucks are among the most popular of vehicles sold in the United States. Each includes a cabin, a bed section for carrying cargo, and a swinging tailgate to retain cargo in the bed. The tailgate assembly is generally formed in a metal forming operation from stamped metal panels which are welded together to form the tailgate. The tailgate as presently used in pickup trucks is a relatively heavy assembly, weighing about 50 pounds. The assembly is made from a number of stamped steel sheets that are joined together by resistance spot welding. Steel reinforcements are welded to the sheets, adding strength and rigidity at critical locations.
The tailgate needs to be as light as possible for ease of use and so that the truck's payload can be increased without sacrificing fuel economy. Currently available tailgates are heavy because they are made from steel. In addition, they are assembled from many components and are not as reliable, strong, or durable as desired. The steel panels are also subject to attack by moisture, road salt, and other chemical agents in the environment that are corrosive to steel and eventually detract from its structural integrity and appearance. Accordingly, there still remains a need to provide a lightweight, strong, durable panel for pickup truck tailgates that has minimal impact upon vehicle cost. It is also desirable to reduce tailgate weight in order to improve fuel efficiency and truck payload capacity.
In recent years, some vehicle body panels have been made from thermoplastic polymers. Such panels are lighter than steel sometimes provide reduced strength and rigidity compared with steel panels. It has been generally assumed that tailgates needed to be made from steel to provide the durability and surface finish desired by today's consumers. Because the tailgate assembly is used as a loading platform when in the lowered position, it must be strong enough to support a substantial weight. Merely substituting plastic components for the steel inner and outer panels of existing tailgate designs do not provide sufficient strength to meet this load requirement.
Advances in materials, paints and molding techniques now enable the manufacture of a tailgate that meets the surface finish requirements of a vehicle exterior surface. The materials make a molded tailgate visually indistinguishable from a painted steel tailgate.
Accordingly, a method of making a molded polymer tailgate to a pickup truck is provided which reduces weight and costs without sacrificing strength.